April 22, 2010
Dissolving plant biomass in "green" solvent ionic liquids - salts that melt at low temperatures - converts more sugars needed for biofuel more quickly than traditional methods, according to a new study by Colorado State University professors.
Eugene Chen, professor of chemistry and the co-author of a study published in Energy & Fuels.
The discovery is an important step in the move toward the use of nonedible plant biomass as an alternative source for fuel. The study, by Professor Eugene Chen in chemistry and Xianghong Qian, an assistant professor in mechanical engineering, was recently published in the April 15 issue of American Chemical Society’s journal, Energy & Fuels.
Traditionally, plant biomass materials need enzymes or strong acids as catalysts to release the sugars locked within walls of plant cells. When mixed with a suitable amount of water, ionic liquids – called “green” solvents because they’re nonvolatile and recyclable – convert the biomass directly into sugars. This process is completed without added acid catalysts that are commonly used in other processes to extract sugars from plants.
The sugars extracted from plant biomass can be readily converted into HMF - 5-hydroxymethyl furfural, which leads to biofuel with considerably higher energy density than current ethanol-based biofuel. The new process they developed can also convert the biomass directly into HMF in high yield, without isolating the sugars.
“Extracting that sugar and subsequently converting it to biofuel can be costly – one-third of the cost of the entire process is the enzymes,” Chen said. “While that process does have some unbeatable advantages – it can convert cellulose to glucose almost exclusively - the cost of it is high and the rate of the sugar release is low.”
Xianghong Qian, an assistant professor in mechanical engineering and the study co-author.
The cost of ionic liquids can be steep as well but they can be recovered, recycled and reused, Chen said. Qian, through computer modeling, helped Chen determine that the origin of the acidity discovered in ionic liquid-water mixtures. This acidity was previously unrecognized and now found suitable for conversion of biomass into sugars also without common side reactions – no additional catalyst was needed.
Ionic liquids are among the very few liquids that can dissolve plant biomass since plants have very tight defense systems that make it difficult to break down cell walls. The support system of the plant is intertwined with the sugars needed for biofuel, lignin, and other proteins.
If scientists could get to the sugars in plants easily, then they could meet society’s energy needs through Earth’s plants, Chen said.
“In about one decade, plant biomass could sequester the energy equivalent of the energy stored in all the crude oil on Earth. The problem is that we currently cannot efficiently and economically convert the biomass into sugars or directly into fuels,” he said.
Chen, a former senior research chemist with Dow Chemical, has been at Colorado State since 2000. Qian joined Colorado State in 2006 from the National Renewable Energy Laboratory where she researched biomass conversion to biofuels using thermochemical methods.
Also assisting with the research are Yuetao Zhang, a research scientist working with Chen, and Hongbo Du, Qian’s graduate student.
Contact: Emily Wilmsen
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